The behavior of Japanese common squid Todarodes pacificus under a squid jigging boat (research vessel Hakusan-maru, 167 gross tons) was investigated with echosounder and sonar during jigging operations in the Sea of Japan. Shipboard metal halide lamps (234 kW) were lit at night, and operations were conducted until enough squid had been gathered. Thereafter, an underwater light emitting diode lamp (600W) was set under the boat and turned on/off. A shaded area was formed under the boat by the light of shipboard lamps, but it was partially eliminated and deformed by the light of the underwater lamp. Many squid were in the shaded area before the underwater lamp was turned on, but almost all the squid located near and above the lamp moved away from the area immediately after the lamp was turned on. Catch per unit effort (CPUE) decreased markedly while the underwater lamp was lit. Thereafter, when the underwater lamp was turned off, the squid immediately gathered in the shade area and CPUE also increased. These results indicate that the shaded area formed by the light of shipboard lamps gathers the squid under the jigging boat and helps to capture them.

The aim of this study is to investigate the use of bentonite to control histamine (Hm) in commercial fish sauce and model fish sauce. Addition of bentonite at 0.1 to 30% (w/v) to commercial fish sauce resulted in an increase in Hm adherence and adsorption followed by increasing amount of additive bentonite. In the commercial fish sauce, the adhered and absorbed Hm content began to increase immediately after the addition of bentonite, and equilibrium was not attained for Hm adherence and adsorption for about 3 h. The effect of temperature (10-100°C), pH (2.0-8.0) and NaCl concentration (5-25%) on Hm adherence and adsorption in model fish sauce with bentonite was investigated. The lower the temperature and pH, the higher the Hm adherence and adsorption. However, there was no significant difference (p>0.05) in the adhered and adsorbed Hm content in the range of 5 to 25% NaCl. These results suggest that Hm level in fish sauce can be effectively reduced with bentonite.

The behavior of Japanese common squid Todarodes pacificus around a squid jigging boat during night-time operation was investigated. Eighty-nine operations were conducted by R/V Hakusan-Maru (167 gross tons) equipped with 78 metal halide lamps (234 kW in total) in offshore fishing grounds in the Sea of Japan, and sonar images and squid catch were continuously recorded (logged). The positions of squid schools before they were caught were tracked from sonar image recordings using digitizer software. Squid schools moved around the boat, gradually approached the boat and then tended to locate in fore and aft areas just before they were caught. More squid were caught by jigging machines near the bow or stern than by those near the center of the boat. Underwater irradiance was lower in fore and aft areas than in port and starboard areas. These results indicate that squid schools tended to enter under the boat through fore and aft areas. Namely, fore and aft areas with low irradiance are thought to function as an entrance to the shaded area under the boat for the squid.

The distribution of juveniles of Japanese common squid (Todarodes pacificus) autumn cohort and its relation to oceanographic conditions were analyzed to see if they can be used to accurately forecast the stock size. Research cruises was conducted using a total of 5 research vessels during 2001-2010 in April in the southern Sea of Japan. Juveniles were caught in 267 of 331 tows of a trawl net at approximately 0-10 m depth, and the numbers caught in each tow ranged from 0 to 1087. Samples were divided into the autumn and winter cohorts based on the dorsal mantle length (DML). The autumn cohort was abundant (40 inds / tow) where the sea surface temperature ranged from 10 to 11 °C and less abundant in warmer water. This cohort was more abundant in offshore areas, while the winter cohort was more abundant near shore. The mean catch of the autumn cohort was used as an index of the annual abundance of juveniles. This index and the stock size were significantly correlated. These results suggest that the stock size of the T. pacificus autumn cohort can be forecasted before the fishing season based on the abundance of juveniles, but this relationship is highly uncertain due to observational errors.

Fukudome K.-I.,Japan National Research Institute of Fisheries And Environment of Inland Sea | Igeta Y.,Japan National Research Institute of Fisheries And Environment of Inland Sea | Senjyu T.,Kyushu University | Okei N.,Ishikawa Prefecture Fisheries Research Center | Watanabe T.,Japan National Research Institute of Fisheries And Environment of Inland SeaContinental Shelf Research | Year: 2016

The effectiveness of a light emitting diode (LED) fishing lamp consisting of 950 oval-shaped blue LEDs was investigated in offshore fishing grounds for the Japanese common squid Todarodes pacificus in the Sea of Japan. Squid jigging operations were conducted by R/V Hakusan-Maru (167 gross tonnes) equipped with 216 LED lamps and 78 metal halide (MH) lamps. Mean catch per unit effort was markedly lower in operations using only the 216 LED lamps (15 kW in total) but slightly lower in operations using both the 216 LED lamps and 24 MH lamps (87 kW in total) than using the 78 MH lamps (234 kW in total). The light from MH lamps widely spread in the sea surface layer but that from the LED lamps irradiated only a limited area near the vessel, suggesting that light distribution affected catch performance. Fuel consumption of the generator engine for lighting these lamps was proportional to the total electric power consumption of the lamps. Fuel consumption for lighting both the 216 LED lamps and 24 MH lamps was 37% of that for lighting the 78 MH lamps. These results indicate that fuel can be saved by the combined use of LED and MH lamps without a remarkable reduction of squid catch.

Although the top shell Turbo (Batillus) cornutus (Turbinidae) is a well-known and industrially important shellfish species in Japan, the diploid chromosome number and karyotype of this species have not been previously elucidated. In this study we investigated the diploid chromosome number and performed karyotype and fluorescence in situ hybridization (FISH) analyses of the telomere sequence on chromosomes of T. cornutus. A diploid chromosome number of 36 was identified in larval somatic cells, and the karyotype comprised 16 pairs of metacentric and 2 pairs of metacentric/submetacentric chromosomes. In the telomere FISH analysis using a vertebrate telomere probe, fluorescein isothiocyanate-positive hybridization signals were clearly observed on the telomeric regions of the chromosomes. This result suggests that the FISH technique is appropriate for other Turbinidae species and that the telomere sequence of T. cornutus is (TTAGGG)n, which is the same as that of vertebrates.